The effect of the 7R allele at the DRD4 locus on risk tolerance is independent of background risk in Senegalese fishermen

It has been shown that living in risky environments, as well as having a risky occupation, can moderate risk-tolerance. Despite the involvement of dopamine in the expectation of reward described by neurobiologists, a GWAS study was not able to demonstrate a genetic contribution of genes involved in the dopaminergic pathway in risk attitudes and gene candidate studies gave contrasting results. We test the possibility that a genetic effect of the DRD4-7R allele in risk-taking behavior could be modulated by environmental factors. We show that the increase in risk-tolerance due to the 7R allele is independent of the environmental risk in two populations in Northern Senegal, one of which is exposed to a very high risk due to dangerous fishing.


Novelty seeking
Task We asked participants to choose one of two options. The first option was to drink one glass of a well-known and well recognizable soda. The second option was to drink two cups of a "novel" soda, which was prepared by the research team and was a mixture of a famous brand of soda and fruit juice.
The variable N ovelty is defined as a dummy variable equal to 1 if the participant chose the novel soda.

Observations 661
Note: The outcome variable is novelty seeking. The variable for novelty seeking is a choice between two beverages, one being a standard easily recognizable, and the other being a new soda, unknown to participants. Standard errors in parentheses. The coefficients are the results of a Probit estimations. The sample is pooled (non-risky and risky areas). Student's t-test * p<0.10, ** p<0.05, *** p<0.01.  primers and GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAG for reverse primers, see Table S.8 for SSR localization on human chromosome and Table S.7 for primer list.

Analysis of genetic differentiation between zones
Amplification of all primers pairs was realised independently on a DNA pool of 10 individuals. The PCR was prepared in a final volume of 10 µL containing 2 µL of 5X Hot FIREpol Blend Master Mix (Solis Biodyne, Tartu, Estonia), 1 µL of 2µM primer pairs, 1 µL of the DNA pool (14 ng/µL) and 6 µL of PCR-grade water. The PCR conditions consisted of an initial denaturation at 95°C for 15 min followed by 35 cycles of denaturation at 95°C for 20 s, annealing at 59°C for 60 s, extension at 72°C for 30 s, and a final extension step at 72°C for 10 min. The amplification of each primer pair was assessed on 3% agarose gel electrophoresis. Primer pairs that did not amplify or showed an non-specific profile were removed from further analyses.
Genotyping analyses Genotyping analyses included 95 DNA samples in replicates (including a negative control) to select loci that produced repeatable genotypes for the final genotypic data set.
Participants performed the task only once. Binswanger (1980) found no evidence that learning played a role when the task is repeated, therefore the single trial set up has become standard practice in experimental economics (see for instance Dave et al. (2010) or Holzmeister and Stefan (2021) for lab experiments, and Barr and Genicot (2008) or Strobl and Wunsch (2021) for field experiments).

Income as a confound
Method One potential confound for our results could be that the effect of the 7R allele on risk-tolerance is confounded by an effect of income on risk-attitudes. To test for this, we performed the same regression as in our main specification, adding income as a control.
However, a large fraction of our sample (29%) answered "I do not know" when asked about their income, and their answers were therefor noted as missing values. To cope for this, we used two methods for imputation. First, a Lasso estimation using all other information available in the data set (other than genotype and risk-attitudes). Second, we used a random forest algorithm (Stekhoven and Buehlmann, 2012) using, again, existing other characteristics. Both methods enabled us to create a variable called "Predicted income", equal to the value when reported, and equal to the imputed value when missing.
Results Results are presented in Table S.9. First, we can see that income is not correlated with risktolerance in any specification.
Second, when controlling for income in addition to age, education and living area, the effect of the 7R allele on risk-tolerance is no longer significant. However, the much smaller sample could be a reason to worry, which is the reason why we imputed the value of income for missing values.
Third and most importantly, when predicting the income for missing values using Machine Learning algorithms, we find similar results to the main specification, i.e. the 7R allele has an additive effect, no dominance effect, and there is no significant interaction effects between the living area and the effect of the 7R allele. The magnitude of the effects of the 7R allele is unaffected by the addition of income as a control.